APPLICATION OF X-RAY PHOTOELECTRON SPECTROSCOPY IN CONNECTING THERMAL MATURITY OF KEROGEN TO ITS DIELECTRIC CONSTANT IN ORGANIC-RICH MUDROCKS

摘要

Thermal maturity controls electrical properties of kerogen such as electrical conductivity and dielectric permittivity. Imprecise estimation of these properties results in significant uncertainties in the interpretation of well logs for reserves evaluation. Quantifying the impacts of thermal maturity and chemical composition of kerogen on dielectric constant leads to improved interpretation of dielectric logs. In a recent publication, we showed that thermal maturity of kerogen can significantly affect its dielectric properties and estimates of water-filled porosity. However, a quantitative relationship between thermal maturity and dielectric properties of kerogen, which is required for well-log- based model development in organic-rich mudrocks, is yet to be investigated. The objectives of this paper include (a) quantifying the correlation between thermal maturity and dielectric constant of kerogen through laboratory measurements and (b) linking chemical composition of kerogen to its dielectric constant. To achieve the aforementioned goals, we developed a microwave setup to measure the dielectric constant of kerogen at different thermal maturity levels. We used X-ray photoelectron spectroscopy (XPS) to analyze the elemental composition and to quantify the effects of thermal maturity on the chemical composition of kerogen. We performed measurements on kerogen samples from two organic-rich mudrock formations. We observed that the dielectric constant increases significantly with thermal maturity in both formations. The XPS measurements also showed an increase in the aromatic carbon concentration with thermal maturity, which could explain the increase in the dielectric constant. We then directly quantified the relationship between aromatic content and dielectric constant of kerogen in the two formations. The outcomes of this paper enable selecting reliable dielectric constant values for kerogen as inputs to dielectric models for well-log interpretation. Reliable assumptions for kerogen dielectric constant improve well-log-based interpretation for fluid saturations. In field applications, XPS measurements performed on rock cuttings, could be used for selecting a reliable dielectric constant for kerogen. This enables real-time quantification of the influence of kerogen on dielectric measurements, which improves interpretation of these measurements.